Australia has said it remains committed to resettling 12,000 Syrian refugees, but warned painstaking security checks could take more than a year.

The government said in September that the refugees would be resettled as quickly as possible, but Liberal MP Cory Bernardi said the cabinet should rethink that commitment in light of the risk that terrorists could pose as refugees.

Peter Shergold, co-ordinator general for refugee resettlement in New South Wales, told Australian Broadcasting Corporation the resettlement process could take from 12 to 18 months because of the careful screening.

"I'm working on the basis that the vast majority will come next year and it will probably be over 12 or 18 months, not six months," Mr Shergold said.

The Syrian refugee intake is on top of Australia's usual annual intake of 13,750 refugees from around the world.

Defending the resettlement decision, Mr Morrison told Sydney radio 2GB: "These would have to be, arguably, the most screened group of people you could think of."

And Mr Keenan said: "Taking 12,000 people from Syria was the right thing to do several months ago and it's still the right thing to do today."

Debate over the Syrian refugees was rekindled as an opinion poll showed 44% of respondents thought Australia should take fewer than 12,000 refugees from Syria. Another 27% said 12,000 was about right and 22% said Australia should accept a larger number.

The poll by Sydney-based market researcher Newspoll and published in The Australian newspaper was based on a weekend survey of 1,573 voters nationwide. It had a three percentage point margin of error.